Monitoring and control system



Ot- 5, 1942 A. B. Du MONT ET AL MONITORING AND CONTROL SYSTEM Original Filed July 1o, 1939 2 Sheets-Sheet 1 Oct. 6, 1942. A. B. DU MONT ET AL MONITORING AND CONTROL SYSTEM Crginal Filed July 10, 1939 2 SheeLs-Sheet 2 Svb KME-Jai( UDM,

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Patented Oct. 6, 1942 2,291,752 MoNrroalNG ANn CONTROL SYSTEM Allen B. Du Mont and Thomas T. Goldsmith, Jr., Upper Montclair, N. J., assignors to Allen B. Du

Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Original application July 10, 1939, Serial No. 283,548. Divided and this application August 3, 1940, Serial No. 350,216

3 Claims. (Cl. 179-1715) Our invention relates to improvements in systems and apparatus for -monitoring and signallevel control. A

This application is a division of our copending application, Serial No. 283.548. led July 10, 1939, Patent No. 2,229,556.

For the purpose of monitoring percent modulation of transmitters, it is customary to employ a cathode-ray tube oscillograph. When it is observed, from the monitor pattern on the fluorescent screen, that the signal-level is too high, manual adjustment of the associated amplier is made to reduce the output-signal-level and thus prevent over modulation of the transmitter.

One of the objects of our inventinon is to provide an improved system andi apparatus for monitoring and signal-level control whereby over modulation of a transmitter is prevented by automatic adjustment of the associated amplifier.

Other objects and advantages will hereinafter appear.

For the purpose of illustrating our invention, an embodiment thereof is shown in the drawings, wherein Figure l is a simplified, diagrammatic view oi a system constructed and operating in accordance with our invention;

Fig. 2 is an enlarged, detail, sectional View, the section being taken on the line 2-2 in Fig. 1; and

Fig. 3 is a view similar to Fig. l, showing a modification.

The basic principle involved in the disclosed embodiment of our invention resides in the fact that certain substances or materials yield a greater number of electrons of secondary emission when bombarded by primary electrons, than certain other substances. For example, there is a dilerence between the respective degrees of secondary emission from aluminum and carbon, or from silver and glass, when screens of these materials are bombarded or scanned by a ray or beam of electrons under the same operating conditions.

In Fig. l, the reference numeral III designates generally a monitor device in the form of a cathode-ray tube, comprising an evacuated tube tI having in the neck portion thereof an electron .gun of a conventional construction for developing a ray or beam I2 of elecrons directed at and focused on a screen or `target; I3 at the other end of the tube. The screen I3 comprises a base plate I4 of aluminum foil to which a supporting contact I5 is electrically connected. The

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aluminum plate I4 may be backed by a suitable plate to impart suflicient, rigidity, as will be well understood. A coating I6 of carbon ink is applied to the central portion o'f the aluminum surface, as represented in Fig. 2. Upon the coating of carbon ink, fluorescent material is applied to form a rectangular, fluorescent screen For the purpose of monitoring, a sweep circuit I8 applies a suitable wave to one of the deflecting plates I9, whereby the pattern is spread out in the usual manner for observation and analysis.

The signal to be observed is applied by the connection 2U to one of the deecting plates 2l. In operation, therefore, the deecting means I8,

I9 cause deection of the electron beam I2 in one sense or direction, and the deflecting means 2l causes deection of the beam in another sense or direction, whereby the monitor pattern, represented in Fig. 2 by the reference numeral 22, appears on the uorescent screen Il. As the target or screen structure I3is scanned by the electron beam I2, a signal is developed which may be taken directly from the target by the output line 23. The monitor device is provided with a collector ring 24 adjacent the target, and from which the signals may be taken by the output connection 25.

The signals taken from the collector ring 24 will be of polarity opposite to that of the signals taken directly from the target itself. Having either polarity available is an advantage.

If the operating action of the monitor device ID occurs outside of a predetermined range, or to a predetermined extent, the desired control signal will appear in the output line 23. For example, if the beam I2 is deflected by the plates 2| beyond the physical extent of the fluorescent screen Il, such as to either or both of the dash lines 26, the electrons will bombard the coating I6 of carbon ink, and due to the changed amount of secondary emission occurring in such case, a signal of changed intensity will appear in the output line 23.

In Fig. 1, the signal to be monitored is an audio or video signal from a source represented at 26. This signal passes through an amplifier 21 to a modulated stage 28 in which a carrier from a source 29 is modulated. The modulated carrier is transmitted by a suitable transmitter represented at 3U.

The signal to be observed, in this case, is the modulated radio-frequency at 3l, the latter being supplied from the modulated stage 28 through the connection 32.

The reference numeral 33 designates an automatic signal-changing circuit, which may comprise any suitable and 'Well-known means for changing the signal-level output from the amplifier 21. For example, this means or unit 33 may embody a servomotor which is responsive only to a control signal from a suitable relay 34 supplied through an ampliiier 35 from the output line 2 of the'monitor device I0.

The arrangement and adjustments in our improved system are such that, as long as modulation o'f the transmitter 30 is within 100%, the monitor pattern 22 is within the physical extent of the fluorescent screen I1, and in the output line 23 from the monitor device I0 there is no signal which is eiective to cause operating action of the relay 34. However, if the monitor pattern goes beyond the edge of the fluorescent screen, under which conditionthe electrons of the beam i2 will bombard the carbon-ink coating I6, the signal occurring in the output line 23 will be of changed intensity so as to cause operation of the relay 34 and consequent operation of the unit 33 in a step-by-step fashion until the signal-level output of the amplifier 21 is changed to the point whereat the monitor pattern 22 is again within the physical extent of the fluorescent screen I1.

A warning device, represented at 36, and which may be audible or visual, may be controlled from the relay 34 and caused to operate when the unit 33 is caused to function, that is, when modulation of the transmitter 30 approaches or reaches 100%.

Considering one of the broader aspects of our invention, the output connection 23, the amplifier 35, the relay 34, and the level-changing unit 33, may be considered as constituting feed-back connecting means from the monitor device i to the amplifier 21.

Although the disclosed embodiment of our invention relates more particularly to a system for automatically preventing over modulation of a transmitter, the invention may be embodied in systems for other purposes. For example, the device i0 may be used in a system wherein the pattern 22 on the iiuorescent screen would be a true representation of the heart-beat of a patient, such as in the system disclosed in the Patent 2,221,398, November 12, 1940, to William A. Geohegan. In such case, the arrangement and adjustments might be such that if the heart-beat or pulse exceeds a given value, whereat the pattern 22 goes beyond the physical extent of the fluorescent screen, the resulting control signal in the output line 23 is eiective to cause actuation of a relay, such as the relay 34, or actuation of a warning device, such as the device 36. In this way, the required medical apparatus may be automatically controlled to correct for the abnormal pulse, or an audible or visible signal given whereby the attending surgeon is instantly appraised of the patients abnormal pulse condition.

'I'he principle and operating action in the embodiment of our invention shown in Fig. 3, is the same as that in Figs. l and 2. In Fig. 3, the various parts, units and connections, corresponding respectively to those in Figs. 1 and 2, have been designated by the same respective reference numerals, but with the suffix a, as those in Figs. l and 2. Fig. 3 shows a sound system, in which the amplifier 21a corresponds to the amplifier 21 in Fig. 1, and the associated microphone 26a corresponds to the source 26 in Fig. l. In operation,

if the output-signal-level of the amplifier 21a exceeds a predetermined value, a. control signal appears in the output line 23a from the monitor device Illa, in the same manner and for the same reason as in Figs. 1 and 2. This control signal,

i as in Fig. 1, is effective to cause actuation of the relay 34a, in step-'by-step fashion, until the output-signal-level of the amplifier 21a is changed or restored to the desired operating level. .From the foregoing, it will be seen that in our improved system, the device I0 serves a double purpose, namely, that of a monitor. and that of a selective, overload-relay.

Various modications, within the conception of those skilled in the art, are possible without de-4 parting from the spirit of our invention, or the scope of the claims.

We claim as our invention:

1. In an automatic amplitude control system, a cathode-ray tube having a'screen surface comprising a central fluorescent portion having one secondary emission characteristic andad jacent portions having a dliIerent secondary emission characteristic, means for causinganf electron beam to scan said portions, means for causing said scanning to be controlled by a signal to be monitored, said screen portionsbeing so disposed that overscanning from said central portion to any part of said adjacent portions will produce a change in secondary electron vemission, means for developing a control .potential in re-A sponse to said change in secondary electron emission, and meansfor controlling said iirst named signal in accordance with said control potential.

2. In an automatic amplitude control system. a cathode-ray tube having a screen surface comprising a central uorescentportion having one secondary emission characteristic and adjacent portions having a diiier'ent secondary emission characteristic, means 'fpxfi causing an electron beam .to scan said portions, means for causing said scanning to be controlled by a signal to be monitored, said screen portions being so disposed that overscanning from said central portion to any part of said adjacent portions will produce a change in secondary electron emission, means 'for developing a control potential in resp-onse to said change in secondary electron emission, and

means for controlling said first named signal in accordance with said control potential, said screen surface providing for visual observance of said first named signal.

3. In an automatic amplitude control system, a cathode-ray tube having a screen surface comprising a central uorescent-l portion ,having one secondary emission characteristic and adjacent portions having a different secondary emission characteristic, means for causing an electron beam to scan said portions, means for causing said scanning to be controlled by a signal to be monitored, said screen portions being so disposed that overscanning from said central portion to any part of said adjacent portions will produce a change in secondary electron emission, means for developing a control potential in response to said change in secondary electron emission, and means for controlling said rst named signal in accordance with said control potential, said last named means including relay means controlled from said output circuit and being responsive only to such control signal.

ALLEN B. DU MONT. THOMAS T. GOLDSMITH, J R. 

